A little background: since our Stangs are unibody and don’t have a chassis, the load is carried by a combination of components. The rear sub frames extend from the tail to an area under the rear seat. From there they are connected by the rear torque boxes outboard to the rocker panels. The rockers and floor bear the center load along the bottom of the car. If you have a coupe or fastback, some of this load is spread to the roof. If you have a convertible, an inner rocker is added back to back with the outer rocker to compensate for the absence of the roof. The rockers extend to the just behind the front tires, where the front torque boxes connect the load back inboard to the front sub frame. I’ve been investigating how to install convertible inner rockers in my fastback. Street or Track did a good article showing how to upgrade a coupe/fastback https://streetortrack.com/Installing-convertible-rockers-into-a-65-68-p-14.html, but they noted that they ran into a problem that is seemingly on virtually all unmodified cars. The inner rocker they used is a straight box approximately 2.5 x 5.75 x 75. They found that just behind the front torque box (about 10” from the front of the rocker), the outer rocker began to angle up and was about 1/2” too high at the front. Since their new inner convertible rocker was straight, it was off by 1/2” at the front and they had to take measures to weld it properly, since the pinch welds were no longer in a position to weld to. I put a straight edge under the pinch weld on my Mach and found the same condition- it angles up in the front 10” or so of the rockers. I have a southern California car where it rarely rains and was always garaged. She’s a survivor that has very little rust. You would be hard pressed to find a better preserved car. Here is my theory: I believe that the outer rockers on all our cars fatigue and bend just behind the front torque box. Think about it and it makes sense- most of the weight is in the front, and the weakest point would be right behind the torque box. Following that thought weight wise, I have a 351w with an FMX, and relatively low mileage on the body of the car at 73k. Suffice to say, that if mine does it, most of them do. So I’m wondering if anyone knows if NEW replacement outer rockers are straight along the lower pinch weld area? Pictures of parts appear to be straight. If so that pretty well proves that the cars fatigue and sag over time. What the heck, they are only 10 times past their expected design life.